I was also very sketchy about that part..i mean ofc their were many insignificant incidents there but this particular part has shown this special bond they both share(Hanzawa n Tashiro). And also Hanzawa is always so chill but with Tashiro he just gets all pushy and shows off his rights ordering around. First I just thought they were normal sempai kouhai but for some reason a romantic relationship makes more sense..(this might be just my bl fan brain but it really does make sense)